1. Field of the Invention
The present invention relates to a magnetoelectric generating system employing a synchronous magnetoelectric generator to generate electric power of a fixed output voltage.
2. Description of the Prior Art
FIGS. 1 and 2 are a sectional front view and a sectional side view, respectively, of a conventional synchronous magnetoelectric generator. The synchronous magnetoelectric generator has a frame 31, a rotor shaft 36, bearings 32 and 33 supporting the rotor shaft 36, a stator core 34, a stator coil 35 (output coil), and permanent magnets 37 fixed to the rotor shaft 36 to create a rotating magnetic field. The stator core 34 and the stator coil 35 constitute an armature.
In operation, a magnetic flux produced by the synchronous magnetoelectric generator is dependent on the operating characteristics between the magnetic flux density B of the permanent magnets for creating a rotating magnetic field, and magnetomotive force H, and the output voltage of the magnetoelectric generator fluctuates according to the load current. The lagging current among the components of the load current has demagnetizing effect that reduces the output voltage. The leading current has magnetizing effect that increases the output voltage. Accordingly, the output voltage characteristics of the synchronous magnetoelectric generator are dependent on load power factor and the synchronous magnetoelectric generator is unable to maintain its output voltage constant. Therefore, the synchronous magnetoelectric generator has been applied to limited purposes for which the synchronous magnetoelectric generator need not be controlled and voltage fluctuation is not a problem. It has been known to use a Zener-diode voltage regulator circuit in combination with a synchronous magnetoelectric generator of a comparatively small capacity as shown in FIG. 3 to provide power of a constant voltage.
Shown in FIG. 3 are a synchronous magnetoelectric generator 1, a voltage detector 5 for detecting the voltage across the two phases of the synchronous magnetoelectric generator 1, breakers 9 provided in lines for the phases, respectively, a prime mover 10 directly coupled with the synchronous magnetoelectric generator 1 with a shaft coupling, a load 11, three pairs of Zener diodes 40, and limiting resistors 41. The two paired Zener diodes 40 are connected reverse to each other between the two phases. If the output voltage of the synchronous magnetoelectric generator increases beyond a fixed value, one of the two paired Zener diodes 40 becomes conductive for voltage peak clipping, so that a constant voltage is applied to the load 11.
Since the conventional synchronous magnetoelectric generator has such characteristics, peak voltage clipping is necessary to obtain a constant voltage. Therefore, the operating efficiency of the synchronous magnetoelectric generator is very low, and the synchronous magnetoelectric generator is unable to recover the voltage when the voltage tends to drop due to variation in the load. Techniques similar to such a conventional synchronous magnetoelectric generator are disclosed in Japanese Utility Model Publication No. Sho 60-3670.